Sewage treatment



Nov. 18, 1941. c

SEWAGE TREATMENT Fil ed Sept. 24, 1938 2 Shee ts-Sheet \1 Nov. 18, 1941.H. BACH 2,263,451

SEWAGE TREATMENT Filed Sept. 24, 1938 2 Sheets-Sheet 2 IN VEN-T OR.

Maw/jack Patented Nov. 18, 1941 SEWAGE TREATMENT Hermann Bach, Berlin,

International Filter Co.,

ration of Delaware Application September In Germany scum.

This invention relates to the treatment oi sewage, sewage sludge andsimilar materials. and in particular to the anaerobic digestion oi suchmaterials.

It is a general object of my invention to improve the removal andclarification oi sewage sludge supernatant or the like in a treatmentinvolving separate digestion. A particular object is to apply suchimproved treatment to the finely divided and slowly settling sludgeparticles suspended in digester supernatant liquor. Another object is toprovide a separate settling space within a digester chamber, and inparticular, in combination with the root of the same, which roof may beeither fixed or floating. Still another object is to provide a treatingplant including such a digester chamber with supernatant settling space,and suitable devices cooperating with said digester chamber and adaptedto cooperate with said settling space; v

The art of constructing and operating sewage treating plants andparticularly, the construction and operation oi digester chambers is ahighly complex field. It is impossible and unnecessary in thisspecification to restate all oi the pertinent considerations andcomplications;

but. persons skilled in the art will be aware oi the same as certainstandard elements 01 pertinent apparatus and methods will be referred toin the iollowing, in combination with elements which are proposed-torthe first time, in this connection. The advantages oi the newcombinations proposed will be obvious on such consideration.

In the drawings, I

Fig. 1 shows one embodiment oi my invention in sectional side elevation.

- 2 gives a plan view oi apparatus shown in Fig. 1.

Fig. 3 shows a modification in plan view of the apparatus oi Fig. 1, incombination with other parts of sewage treating plant.

Fig. 4 is a iurther modification oi apparatus shown in Fig. 1.

In the drawings, numeral It represents a digester tank constructed oisuitable material and having any suitable shape, ior instance,rectangular as shown in Fig. 2 or circular as shown in Fig. 3. Tank Illhas an inlet ll ior raw sludge or other sludge to be digested and anoutlet I2 for digested sludge. Mixing and/or agitating equipment may beprovided as illustrated at ii. The numeral It indicates a spiral of hotwater pipes as an example oi means ior ,183, October Germany, asslgnorChicago, 111., a corpo- Serial No. 231.408 0, 1m

oi same. in order to provide or maintain suitable temperatures,depending on the particular digestion process desired. Cover II ispreferably, a solid, air-tight cover which may be constructed either infixed relationship to the outer walls oi digester II as shown in Fig. l,or floating on material within digester II as ior instance by means 0!pontoons It shown in Fig. 4. Cover ll may or may not be in contact withthe surface of material in digester it so as to submerge scum or otherfloating matter which may rise to the suriace. Cover II may also carry agas dome II or may otherwise provide for the withdrawal oi' digester gasthrough suitable tubing.

ll. Gas withdrawn through the tubing It may be utilized for the heatingoi water to be applied in pipes It, or for other purposes, for instanceby means ot a burner and heater it.

A typical sewage treating plant including digester It may receive rawsewage through conduit II. The coarse matter suspended or floating inthe sewage may be removed by suitable screens, girt chamber, greaseseparator or similar devices 2! having an eilluent conduit 22 which atthe same time is the influence conduit oi settling or other clarifyingapparatus '28 provided with suitable sludge separating equipment asdiagrammatically illustrated at 24. Clarified sewage irom the settlingapparatus is ordinarily fiows through a conduit 25 to a secondarytreating device 28 which may be in the nature of an activated sludgeplant, trickling filter, submerged filter, or any other means adapted torender the sewage inoiiensive and coniorming with legal to the river,etc. In other cases, however, some device oi this sort will be required,and will have an emuent to such brook, river or lake. as indicated at21. Certain liquid or solid products irom the secondary treatment in thesecondary treating device 28 may be recirculated, ior in= stance to theclariiler inlet 2! by means oi con duit It, as is well known in this.art. This will in turn have a certain eflect on treatment is clarlfierI3 and also on the sludge resulting irom heating digester It or materialtherein or part as such treatment.

This sludge in most cases is intermittently withdrawn'from the settler33 through conduit 33 having a gate, valve or other controlling means 33and communicating with digester infiuent ll. Sludge withdrawal may beeither by means of a pump (not shown) or by gravity or the like.Digested sludge withdrawn through conduit I! may be further treated byany appropriate device 3|.

In practice, digesterv It may receive raw sludge through inlet I I aboutonce or twice a day. When digester I3 is filled to the limit of itscapacity, by such successive or by continuous additions of raw sludge,any further charge of raw sludge requires the previous removal of acorresponding volume of material from digester II. To some extent,digester space can be made available by withdrawal of digested sludgethrough conduit l2. However, such withdrawal should not be had beforethe sludge is fully digested, which may take a period of several daysand even of several weeks. Addition of raw sludge at H must be had inmuch shorter intervals in order to keep clarifier 33 and the remainderof the plant in operable condition, and to provide for proper mixing indigester In. Also, the amount of digested sludge to be withdrawn throughconduit I2 is ordinarily much less and sometimes 8 to 12 times smallerthan the volume of raw sludge received at the inlet I I, due to the factthat digested sludge is rather dehydrated and otherwise freed posed onthe digester sludgewhich forms'and tends to settle in the digester tank.Light matter such as scum or grease may float at the surface of thedigester supernatant, which surface is indicated in the drawings at 32.In certain cases, it may be desirable to agitate or to break up saidfloating matter or scum or even to prevent the formation thereof byagitating means l3, or to similarly act upon the sludge lying in thebottom of digester I0 or to otherwise influence the processes occurringinside digester In in certain ways; and some such interi'ering methodsrender the supernatant in digester I0 quite turbid. Even if suchartificial stirring is omitted, the supernatant will beturbid due to itsinherent characteristics and alsdfi to the fact that the naturalprocesses occurr in digester III will always produce a certain amount ofagitation, stirring up the Sludge from the bottom and carrying downparticles of floating scum, if any.

In view of this condition of the supernatant, the aforementioned usualprocess of supernatant withdrawal at the time of introduction of rawsludge is extremely unsatisfactory. The supernatant withdrawn is a wasteproduct that is particularly hard to dispose of. It is possible toclarify such liquids by sedimentation, and attempts have been made to soclarify the supernatant together with the raw sewage after returning thesupernatant to the main clarifier infiuent of a sewage treating plant.

iorded by the clarifiers of a sewage plant is usually too short toeffect any appreciable clarification of recirculated supernatant, sothat the clarifier eiiluent will become polluted when following thismethod. It has been proposed to enlarge the main clarifier receiving thedigester supernatant in addition -tothe raw sewage, even beyond thatvolume which is required for the ordinary detention of the combinedamounts of raw sewage and digester supernatant, so as to aiford asumcient detention time for the digester supernatant. It has also beenproposed to construct a separate clarification tank for the digestersupernatant, thereby producing 1 clear liquid which may be passedthrough the main clariiier of the sewage treating plant only for the P pOf being posed to secondary treatment. Apparatus constructed accordingto such ideas has been found expensive as to erection and operation.

I propose to provide a compartment 33 within digester tank l3,preferably formed by walls 33 of suitable shape and material dependingfrom roof I! and having a bottom section 35 which communicates with theouter space of digester Ill. The communication may be of any suitabletype, as for instance a slot 36 in the lower portion of the bottom part35, which preferably is formed as a steep hopper. Chamber 33 has thefunction of providing (1) a clarification space for supernatant formedin digester l3, so that a supernatant may be available for withdrawal tothe influent conduit 22, the conduit 23 from the clarifier to thesecondary treating apparatus or the eflluent conduit 21 which is freefrom the objections stated; and (2) a means for the withdrawal ofsupernatant portions at such times as are selected for the introductionof new charges of raw sludge from clarifier 23. Accordingly, the size ofchamber 33 should be at least equal to the volume of raw sludge to beexpected at each filling operation; and preferably the size, shape andconstruction should be such as to allow substantial clarification ofsuch volume of supernatant within the period between any two fillingoperations.

Withdrawal of'supernatant from chamber 33 may be had through a pipe 31by means of a pump (not shown). In order to secure the withdrawal ofclarified supernatant only, instead of a mixture of such supernatant andthe turbid liquor outside of chamber 33, slot 33 is provided with aclosure means illustrated by a beam 33 suspended on rods 33 which extendupwardly through cover l5 and which may have toothed rack portions 43 attheir upper ends, engaging gears ll of a winch 42 so that beam 33 may beshifted to seal the slot 36, or to allow free communication of liquidand solids through the Q same. Somewhat similar means are well knownfrom certain types of settling basins, but have not to my knowledge beenapplied for purposes kindred to the present invention.

A vent may be provided in the chamber, as at 33 so that digester gasformed in compartment 33 may be disposed of.

In normal operation, beam 33 is spaced from slot 36 so that solidssettling in compartment 33 may slide down the bottom walls 35 andthrough slot 36. Sediment falling through slot 36 displaces liquid inthe outer space of digester l0; and such liquid will enter chamber 33,as is well known from the operation of Imhoi! tanks, which in thisrespect are somewhat similar to the present device. Solids from digesterIt will be substantially prevented from entering with liquid enteringchamber 33 due to the well known one-way effect of bottom 35 and slot36. Therefore. the solids concentration in compartment 33 will becomeconsiderably less than in the outer digester space, and ultimatelypractically all the settleable sludge may be discharged from chamber 33.

If now a new charge of raw sludge from clariiier 23 shall beincorporated in the material present in digester It, then ordinarily thewinch 42 will be operated so as to seal the slot 33. An amount ofsupernatant corresponding to the new charge of raw sludge will then bewithdrawn through pipe 31. Thereafter, winch 42 is operated so as tounseal the slot 36 again, resulting in turbid supernatant enteringchamber 33 through the slot. The new charge of raw sludge is thenintroduced through pipe I i and preferably mixed with the other materialby operation of mechanism l3, so that more turbid supernatant will enterthe chamber 33. Finally, another period of normal operation can follow.

Occasionally digested sludge will be removed through sludge outlet II.The solids concentration in digester It! may be higher than isordinarily the case as the process involves the concurrent steps ofclarifying and of turbulently treating sludge to be digested. Therefore,digested sludge may accumulate relatively rapidly, and the generalresults of the digestion process will be improved accordingly.

In continued operation, a layer of scum may tend to form on the surfaceof liquor in chamber 33, but the withdrawal of material through pipe 37may be carried through so as to remove such scum; or it may be broken upby agitation.

Material withdrawn through pipe 37 may be disposed of in any suitableway, some such ways being diagrammatically illustrated by conduits 45,46 and 41, shown in Fig. 3. Of course, provision may be made forsuitable recirculation, for instance for discharging scum from thecompartment 33 into digester I ll direct.

In the modification of Fig. 4 there is shown a control valve 44cooperating with suitable pressure means (not shown) in the gaswithdrawal line l8, and a gas by-pass 43a between compartment 33 and theouter space of digester id. The valve and by-pass cooperate so as toavoid the added buoyancy of floating roof l5 which ordinarily would beexperienced when chamber 33 is emptied while sealed by the beam 38. Onthe other hand, stops 48 are provided as a lower limit for the downwardmovement of cover l5.

Other modifications and amplifications will occur to persons skilled inthe art. For instance, clarification in chamber 33 may be promoted bychemical means. Such modifications and amphfications are all intended tobe covered by the claims which follow.

I claim:

1. Apparatus for sewage treatment comprising a clarifier, a liquidefliuent conduit from the upper portion of said clarifier, means forpurifying liquid eiiluent communicating with said eflluent conduit, ananaerobic sludge digester, a sludge withdrawal conduit from the lowerportion of said clarifier and communicating with said anaerobicdigester, a conduit for the withdrawal of digested sludge from adjacentthe bottom of said digester, partition means forming a compartment insaid digester adjacent the top thereof, means for agitating sludge in anagitation zone in said digester removed from said compartment, an opencommunication adjacent the bottom of said compartment and opening intosaid zone, means for closing said open communication, and a conduit forthe withdrawal of supernatant liquid from-said compartment communicatingwith said means for purifying liquid eflluent.

2. A method of sewage treatment comprising the steps of separatingsludge from raw sewage in a sedimentation zone, purifying the liquideflluent from said sedimentation zone, flowing the sludge from saidsedimentation zone into an anaerobic digestion zone and therebydisplacing a portion of sludge in said digestion zone into asubstantially enclosed anaerobic quiescent settling zone adjacent theupper level of said digestion zone, returning settled solids from saidanaerobic settling zone to the said anaerobic digestion zone, removingclarified liquid from said settling zone, and removing digested sludgefrom said digestion zone.

I 3. A method of anaerobically digesting sludge comprising the steps ofintroducing raw sludge into an anaerobic digesting zone and therebydisplacing a portion of sludge upwardly into a substantially enclosedanaerobic quiescent settling zone within the upper portion of saiddigesting zone, permitting the solids in said sludge in said settlingzone to settle therefrom and to return to the digestion zone,periodically removing clarified supernatant liquor from said settlingzone and periodically removing digested sludge from said digesting zone.

4. In the operation of a sludge digester, the method of removing solidsfrom supernatant liquor within the upper portion of the digester.comprising the steps of non-turbulently displacing a portion of thesupernatant liquor upwardly into a quiescent anaerobic settling zonewithin the upper portion of said digester, retaining the supernatantliquor in said zone for a period sufficient to permit solids to settlefrom said supernatant liquor, permitting the settled solids to descendby gravity into the digestion zone, and periodically removing theclarified supernatant liquor.

5. A sewage treatment plant comprising a clarifier, a conduit for liquideflluent from the upper portion of said clarifier, means for purifyingsaid eiiluent, an anaerobic digester, a sludge conduit from the lowerportion of said clarifier communicating with said anaerobic digester,partition means in said digester providing a substantially enclosedanaerobic settling compartment adjacent the top of said digester, anormally open communication between the bottom of the said settlingcompartment and the digester, means for closing said normally opencommunication, a liquid conduit from said settling compartment, a

digested sludge conduit from the bottom of said digester and a gasoutlet from the top of said into said digestion compartment and adigested sludge outlet.

7. The apparatus of claim 6 wherein the settling compartment is providedwith means for closing the normally open passage in the bottom thereof.

8. A'sludge digester, comprising a tank, parti ticn means within andadjacent the top 01 said tank providing a relatively large primaryanaerobic digestion compartment and a relatively small substantiallyenclosed settling compartment sufrom the top of said primarycompartment, a normally open communication from said primary compartmentinto the bottom of said settlin compartment and adapted to permit theflow of liquid and suspended solids into said settling compartment andto permit the gravitational discharge of the solids settling thereininto said primary compartment. means for closing said communication andan outlet for liquid from said set- 10 tling compartment.

HERMANN BACH.

